The biodiesel as an alternative to diesel is generally produced through transesterification of vegetable oils, animal fats or other non-edible raw materials. The research investigated mixing hydrodynamics of immiscible fluid-fluid by computational fluid dynamics approach. The transesterification fluids composed of crude palm oil, methanol and base catalyst were mixed by a Rushton turbine impeller in a stirred batch reactor of 1 m in diameter and 1 m in liquid height at 60 oC and various impeller rotational speeds (rpm). In order to simulate the turbulent flow field, the mass conservation was governed by the continuity equation and the momentum balance was governed by the Reynolds-averaged Navier-Stokes equation. The turbulence effect was modeled using the k-e model. The model was equipped by two additional transport equations, i.e. turbulence kinetic energy (k) equation and turbulence dissipation energy (e) equation. Mixture model in COMSOL was used to simulate numerically the mixing of these immiscible fluids. The simulation results identified that that turbulence due to the tailed vortex is increasingly significant at higher rotational speeds, the volume fraction of the dispersed phase in the middle of the reactor is more homogeneous at higher rotational speeds.